Three fight for life after asthma storm

Three people are fighting for life following Melbourne's 'asthma thunderstorm', which has been linked to four deaths so far.

Less than 10 people remain in intensive care following the rare weather event on Monday night.

Melbourne hospitals treated more than 8500 patients across Monday night and Tuesday.

Victorian Health Minister Jill Hennessy says senior doctors are amazed there weren't many more deaths given the number of people who suffered cardiac arrest and breathing difficulties during the storm which overwhelmed emergency services and hospitals.

At least four people died during the rare weather and the cause of those deaths will be investigated by the Inspector General for Emergency Management.

His findings will form part of an overarching review that will examine how Ambulance Victoria and emergency services responded, and how the community was notified of the unfolding crisis.